Digital multifunction reprographic systems are well known and have replaced optical reprographic systems as a way to reproduce images. In these conventional digital multifunction reprographic systems, a scanner accepts a document to be copied and converts the document into electronic image(s). These images, usually in the form of pages, are then passed to a central control unit which may re-order or reorganize these pages and then, depending on the request of the user of the device, send the pages or images to a destination. Often this destination is an attached printing unit which makes one or more copies of the original document.
However, these conventional devices perform many other functions besides simple copying. The central control unit is usually equipped with a combination of hardware and software elements that enable it to accept input from other sources. The other sources may include some sort of network interface and/or an interface to a telephone system to enable FAX input.
The network interface is usually configured so that it can accept jobs to be printed from any computer source that is connected to the network. This configuration normally includes elements that can convert input documents formatted in one or more page description languages (PDLs) to the native format of the printing device.
An important inner component of such a conventional multifunction digital device is the image path. This is the combination of software and hardware elements that accepts the electronic images from a multiplicity of sources and performs any operations needed to convert the images to the format desired for the various output paths. The image path is usually one of the more complex and costly components of such digital multifunction devices.
The image path for a conventional multifunction device usually has several constraints. On one hand, there is a desire to make the image path utilize data in a multi-bit per pixel format so as to provide for maximum image quality and a minimum loss of critical information in the transformation of documents from paper to electronic form. On the other hand, there are cost constraints and performance limits on the devices or software that comprise the image path.
Conventional image path electronics may also utilize binary image paths. In this situation, if the input information is scanned in a binary manner at sufficiently high resolution, the scanned image can be reconstructed at the output with little or no perceptible loss of image quality.
Another component of many conventional multifunction devices, especially for those devices having a printing engine that is capable of producing colored output, is the use of analog modulation schemes for the output. In these devices, analog data, in the form of multi-bit pixels, is presented to the modulator of the output printing device. The modulator compares the analog equivalent of the input byte of data to a periodic saw tooth wave. The output therefrom is a signal to the laser imaging component that is pulsewidth modulated by the data stream.
One recent development for conventional multifunction reprographic machines is the use of both binary and analog data in the image path. In such a hybrid image path, the data from the scanner is digitized and converted to binary. All of the intermediate elements of the image path are designed to work with the compact binary data format. Only at the output is the data converted back to multi-bit analog e.g. contone, form.
One way to implement the resolution conversion is to pass the binary data through the digital equivalent of a two-dimensional low pass filter. The low pass filter may replace each pixel in the binary image by the average of the values within some window centered on the pixel of interest. While such a system does an adequate job of converting the high resolution binary data to analog data, these solutions also have the deleterious effect of smearing sharp edges in the original document. Such an effect is particularly detrimental when reproducing text and line art.
A desirable modification to hybrid image paths would be a system wherein the conversion from binary format to analog format could take into account the existence of sharp edges in the image. Ideally such a scheme would be adaptive, that is, it would change its behavior so that it would apply a resolution conversion scheme appropriate to sharp edges for those parts of the image that have such edges, but use a different scheme that was better adapted to more continuous tone parts of the image.
Systems that implement resolution conversion processes, like those outlined above, show significant improvement in image quality compared to systems that do not implement resolution conversion processes. However, such systems are subject to problems. One such problem is the need to somehow distinguish those parts of the image that have edges from those parts of the image that do not. Various processes have been proposed to identify such regions and to develop an image parallel to that being reproduced, a tag image, that identifies those parts of the image that are edges.
All of the above processes deal with the copying process wherein a physical original is presented to the system and the scanner part of the system performs some processing on the digital image of the scanned original to generate the tag information. However, modern multifunction systems are also expected to function as digital printers, accepting input, usually in the form of a page description language format of the document to be printed. There is a component of such systems that converts the page description language form of the document into a form that can be processed by the image path and printing section of the multifunction machine.
If the page description language conversion process generates an analog image directly, any documents to be printed make heavy demands on the intermediate storage parts of the image path. Furthermore, the injection of such an image into the print path may be incompatible with the design of the copy image path which is designed to handle binary encoded image. This incompatibility is undesirable from a cost and performance standpoint. An alternative is to generate the images from the page description language as binary images. This makes the images from the page description language compatible with the copy path, but leaves a problem in that the images from the page description language are not tagged.
However, the page description language “knows” the exact location of any edges, whenever the edges are associated with text or graphics. It would therefore be desirable if the page description language decomposition process could generate edge tags that would be compatible with those tags generated in the copy/scanning process so that images from the page description language would have the same high level of image quality as does the copy path.
However, the page to be printed often contains embedded contone image objects. While the page description language processor has means to process these embedded contone objects, it does not normally contain any means for identifying any sharp edges in these contone image objects and therefore any benefit of edge sharpening cannot be applied to these objects.
One limitation of such a system is that the page description language processor is that it cannot identify the presence of edges if there are image files embedded in the page description language.
Thus it would be desirable to expand the edge detection to include any embedded images as well as the text and graphic components of the page.